Geoid measurement method, geoid measurement apparatus, geoid estimation device, and geoid calculation data collection device

ABSTRACT

A geoid calculation data is collected easily. A geoid calculation data collection device of the present invention comprises an inertial measurement data acquisition part, a comparison data acquisition part, and a recording part. In the inertial measurement data acquisition part, data related to velocity, position, and attitude angle is acquired as inertially-derived data based on an output of an inertial measurement part having a three-axis gyro and a three-axis accelerometer attached to a moving body. In the comparison data acquisition part, data related to velocity is acquired as comparison data from a source other than the inertial measurement part. In the recording part, inertially-derived data and comparison data are recorded in association with each other. In the inertial measurement part, a bias stability is acquired that allows error arising from plumb line deviation to be distinguished to a predetermined degree.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of U.S. patent application Ser. No.17/057,862 filed Nov. 23, 2020, which is a National Phase ofPCT/JP2019/022094 filed Jun. 4, 2019, which claims the benefit ofJapanese Patent Application No. 2018-138406, filed Jul. 24, 2018. Thecontents of these applications are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to a geoid measurement method, a geoidmeasurement apparatus, a geoid estimation device, and a geoidcalculation data collection device for calculating a change in geoidheight or a geoid height by using an inertial measurement part having athree-axis gyro and a three-axis accelerometer.

BACKGROUND ART

The technologies illustrated in literature such as Patent literature 1and Non-patent literature 1 are known as technologies that correct datarelated to a position, a velocity, and an attitude angle calculated fromthe outputs of a three-axis gyro and a three-axis accelerometer based ondata obtained from another sensor or the like. The data obtained fromanother sensor or the like is Global Positioning System (GPS) data inmany cases, but may also be combined with data other than GPS, asillustrated in Non-patent literature 1. FIG. 1 is a diagram illustratingthe “GPS hybrid navigation block diagram (loose cup method)” illustratedin FIG. 4 of Non-patent literature 1.

Non-patent literature 2 is literature describing possibilities in thegeodetic field, providing an explanation of and issues related toelevation, ellipsoidal height, and geoid height, and also illustratingpossibilities when using an optical lattice clock. In Non-patentliterature 2, elevation is described as “the height from mean sea level(geoid) to ground level, determined by leveling”. Ellipsoidal height isdescribed as “the height from an Earth ellipsoid to ground level,determined by GNSS survey”. Geoid height is described as “the heightfrom an Earth ellipsoid to mean sea level, a potential surface such asgravitational potential, with unevenness reflecting the heterogeneity ofEarth's internal mass distribution”.

PRIOR ART LITERATURE Patent Literature

-   Patent literature 1: Japanese Patent Application Laid-Open No.    S63-302317

Non-Patent Literature

-   Non-patent literature 1: Masaki Yamada, Ryutaro Takeuchi, and    Takayuki Okuyama, “Technology and Application Products about GPS    Hybrid Navigation for Inertial Navigation System”, JAE Technical    Report. No. 33. pp. 1-10, March 2010, [retrieved Jun. 12, 2018],    Internet <https://www.jae.com/jp/gihou/gihou33/pdf/g_05.pdf>-   Non-patent literature 2: Toshihiro Yahagi, “Possible Uses of Optical    Lattice Clock in Geodetic Field”. Science and Technology Council    Advanced Research Infrastructure Subcommittee, Quantum Science and    Technology Committee (3rd), pp. 1-14, May 10, 2016, [retrieved Jun.    12, 2018], Internet    <http://www.mext.go.jp/b_menu/shingi/gijyutu/gijyutu17/010/shiryo/_icsFiles/afieldfile/2016/06/23/1372759_6.pdf>

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Non-patent literature 2 indicates that determining elevation by levelingis time-consuming and costly. Furthermore, the possibility of using anoptical lattice clock to determine the elevation at a benchmark isindicated.

As described above, geoid height is an important target of measurement.However, there is no method of measuring geoid height easily.Accordingly, an object of the present invention is to provide a geoidmeasurement method, a geoid measurement apparatus, a geoid estimationdevice, and a geoid calculation data collection device for measuring achange in geoid height easily.

Means to Solve the Problems

A geoid measurement method of the present invention executes an inertialmeasurement data acquiring step, a comparison data acquiring step, astate variable estimating step, and a geoid calculating step. In theinertial measurement data acquiring step, data related to velocity,position, and attitude angle is acquired as inertially-derived databased on the output of an inertial measurement part having a three-axisgyro and a three-axis accelerometer attached to a moving body. In thecomparison data acquiring step, data related to velocity is acquired ascomparison data from a source other than the inertial measurement part.In the state variable estimating step, state variables including a plumbline deviation are estimated by using the inertially-derived data andthe comparison data to apply a Kalman filter in which the plumb linedeviation is included in the state variables. In the geoid calculatingstep, a change in geoid height is calculated based on the estimatedplumb line deviation at an estimated position that the estimatingapplied to.

A geoid measurement apparatus of the present invention comprises aninertial measurement data acquisition part, a comparison dataacquisition part, a state variable estimation part, and a geoidcalculation part. The inertial measurement data acquisition part isprovided with an inertial measurement part having a three-axis gyro anda three-axis accelerometer attached to a moving body, and acquires datarelated to velocity, position, and attitude angle as inertially-deriveddata. The comparison data acquisition part acquires data related tovelocity as comparison data from a source other than the inertialmeasurement part. The state variable estimation part estimates statevariables including a plumb line deviation by using theinertially-derived data and the comparison data to apply a Kalman filterin which the plumb line deviation is included in the state variables.The geoid calculation part calculates a change in geoid height based onthe estimated plumb line deviation at the estimated position that theestimating applied to.

A geoid estimation device of the present invention comprises a recordingpart, a state variable estimation part, and a geoid calculation part.The recording part records inertially-derived data and comparison datain association with each other, the inertially-derived data being datarelated to velocity, position, and attitude angle acquired based on anoutput of an inertial measurement part having a three-axis gyro and athree-axis accelerometer attached to a moving body, and the comparisondata being data related to velocity acquired from a source other thanthe inertial measurement part. The state variable estimation partestimates state variables including a plumb line deviation by using theinertially-derived data and the comparison data to apply a Kalman filterin which the plumb line deviation is included in the state variables.The geoid calculation part calculates a change in geoid height based onthe estimated plumb line deviation at the estimated position that theestimating applied to.

A geoid calculation data collection device of the present inventioncomprises an inertial measurement data acquisition part, a comparisondata acquisition part, and a recording part. The inertial measurementdata acquisition part acquires data related to velocity, position, andattitude angle as inertially-derived data based on the output of aninertial measurement part having a three-axis gyro and a three-axisaccelerometer attached to a moving body. The comparison data acquisitionpart acquires data related to velocity as comparison data from a sourceother than the inertial measurement part. The recording part records theinertially-derived data and the comparison data in association with eachother. Also, the inertial measurement part is characterized by having abias stability that allows error arising from plumb line deviation to bedistinguished to a predetermined degree.

Effects of the Invention

According to the geoid measurement method, geoid measurement apparatus,and geoid estimation device of the present invention, a change in geoidheight can be calculated. According to the geoid calculation datacollection device, data necessary for calculating a change in geoidheight can be collected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the “GPS hybrid navigation blockdiagram (loose cup method)” illustrated in FIG. 4 of Non-patentliterature 1;

FIG. 2 is a diagram illustrating a functional configuration example of ageoid measurement apparatus, a geoid calculation data collection device,and a geoid estimation device;

FIG. 3 is a diagram illustrating an example of a process flow of thegeoid calculation data collection device;

FIG. 4 is a diagram illustrating an example of a process flow of thegeoid estimation device;

FIG. 5 is a diagram illustrating an example of a process flow of thegeoid measurement apparatus;

FIG. 6 is a diagram illustrating a case where an inertial measurementpart equipped with a ring laser gyro having a level of precisioncomparable to existing technology is installed onboard a vehicle, inwhich position, velocity, and angle data are acquired but comparisondata is not acquired:

FIG. 7 is a diagram illustrating an example in which an inertialmeasurement part equipped with a ring laser gyro having a level ofprecision comparable to existing technology is installed onboard avehicle, satellite positioning data is used as comparison data, the sameconfiguration as the geoid measurement apparatus of the presentinvention is used, and state variables including a plumb line deviationand a gravity anomaly are estimated by applying a Kalman filter in whichthe plumb line deviation and the gravity anomaly are included in thestate variables to data obtained from a single run;

FIG. 8 is a diagram illustrating an example of measuring geoid heightbased on the estimated plumb line deviation in the example illustratedin FIG. 7;

FIG. 9 is a diagram illustrating data obtained from 10 runs with thesame configuration as FIG. 6;

FIG. 10 is a diagram illustrating an example of measuring geoid heightwith data obtained from 10 runs with the same configuration as FIG. 8;

FIG. 11 is a diagram illustrating an example of estimating statevariables including a plumb line deviation and a gravity anomaly byapplying a Kalman filter in which the plumb line deviation and thegravity anomaly are included in the state variables to an average ofdata acquired by 100 vehicles with the same configuration as FIG. 8, andestimating geoid height based on the estimated plumb line deviation; and

FIG. 12 is a diagram illustrating an example in which an inertialmeasurement part whose Allan deviation is improved over existingtechnology by an order of magnitude is installed onboard a vehicle,satellite positioning data is used as comparison data, the sameconfiguration as the geoid measurement apparatus of the presentinvention is used, and geoid height is estimated with data obtained froma single run.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail. Note that structural elements having the same function aredenoted with the same signs, and duplicate description of such elementsis omitted.

Example 1

<Apparatus Configuration and Process Flows>

FIG. 2 illustrates a functional configuration example of a geoidmeasurement apparatus, a geoid calculation data collection device, and ageoid estimation device. FIG. 3 illustrates an example of a process flowof the geoid calculation data collection device, FIG. 4 illustrates anexample of a process flow of the geoid estimation device, and FIG. 5illustrates an example of the process flow of the geoid measurementapparatus. A geoid calculation data collection device 100 comprises aninertial measurement data acquisition part 120, a comparison dataacquisition part 130, and a recording part 300. A geoid estimationdevice 200 comprises the recording part 300, a state variable estimationpart 210, and a geoid calculation part 220. A geoid measurementapparatus 10 is a configuration comprising both the geoid calculationdata collection device 100 and the geoid estimation device 200, andcomprises the inertial measurement data acquisition part 120, thecomparison data acquisition part 130, the state variable estimation part210, the geoid calculation part 220, and the recording part 300. Inaddition, the geoid calculation data collection device 100 and the geoidestimation device 200 may also be separate. Note that it is sufficientto realize the geoid measurement apparatus 10, the geoid calculationdata collection device 100, and the geoid estimation device 200 bycausing a processing circuit such as a computer to execute an installedprogram.

The inertial measurement data acquisition part 120 may include aninertial measurement part 110, or the inertial measurement part 110 maybe external to the inertial measurement data acquisition part 120 andtransfer data only. The inertial measurement part 110 is attached to amoving body and has a three-axis gyro and a three-axis accelerometer.The moving body is an automobile, a train, a ship, an aircraft, or thelike. The inertial measurement part 110 may be provided with an internalfunction of converting the outputs from the three-axis gyro and thethree-axis accelerometer into a velocity, a position, and an attitudeangle, or the conversion function may be provided external to theinertial measurement part 110 and internal to the inertial measurementdata acquisition part 120. The inertial measurement data acquisitionpart 120 acquires data related to velocity, position, and attitude angleas inertially-derived data based on the output of the inertialmeasurement part having the three-axis gyro and the three-axisaccelerometer attached to the moving body (S110, S120). “Data related tovelocity” refers to not only velocity data, but also position data andacceleration data. “Data related to position” may refer to a positionrelative to a predetermined fixed point, a position relative to thepreviously measured point (a point that changes every time), or anabsolute position such as latitude, longitude, and altitude. In thisway, such “data related to velocity, position, and attitude angle” maybe the velocity, position, and attitude angle themselves, but is notlimited thereto insofar as the data can be used to uniquely calculatethe velocity, position, and attitude angle.

The inertial measurement part 110 is characterized by having a biasstability that allows error arising from plumb line deviation to bedistinguished to a predetermined degree. The term “plumb line deviation”refers to the difference between the direction of an actual plumb lineon Earth (the direction of a still string on which a weight issuspended) and the normal direction of an Earth ellipsoid. For example,there is a plumb line deviation in the north-south direction and a plumbline deviation in the cast-west direction. In the case of a gyrotypically being used in aircraft at the time of the present application,the error due to the bias stability is large, and therefore the errorarising from the plumb line deviation is ignored. For example, even withthe inertial device hybrid technology illustrated in Non-patentliterature 1, the plumb line deviation in the north-south direction andthe plumb line deviation in the east-west direction are not considered.Furthermore, gravity anomalies are not considered. A “gravity anomaly”is the difference between the actual value of gravity and standardgravity. However, although still in the research stage, if a practicalimplementation of a gyro using atomic waves or ions is achieved, theprecision will be improved by at least an order of magnitude. Inaddition, even with a ring laser gyro (RLG) already in practical use, ifthe diameter is increased by tenfold, the precision could betheoretically improved by a hundredfold. Moreover, the diameter of aring laser gyro can be increased by tenfold and still be installedonboard an automobile or a train. Also, if data repeatedly measured Ntimes on the same path is used, a precision of N^(1/2) can be achieved.Consequently, it is possible to set the bias stability such that errorarising from the plumb line deviation in the north-south direction andthe plumb line deviation in the east-west direction can be distinguishedto a predetermined degree. Note that “to a predetermined degree” meansdeciding the precision of a calculated geoid height, and it issufficient to decide the predetermined degree according to the demandedprecision.

The comparison data acquisition part 130 acquires data related tovelocity from a source other than the inertial measurement part 110 ascomparison data (S130). For example, the comparison data acquisitionpart 130 may acquire satellite positioning data such as GPS data, oracquire data from a source other than the inertial measurement part 110,such as from a speedometer. “Data related to velocity” refers to notonly velocity data itself, but also data from which the velocity can beuniquely calculated, such as position data and acceleration data. Forexample, in the case where the comparison data acquisition part 130captures radio waves transmitted from an artificial satellite, thecomparison data is latitude, longitude, and ellipsoidal height data.Latitude, longitude, and ellipsoidal height data is position data, butif the change over time is calculated, the data can be uniquelyconverted to velocity data. Consequently, latitude, longitude, andellipsoidal height data is also included in “data related to velocity”.

In the case of the geoid calculation data collection device 100, therecording part 300 records the inertially-derived data and thecomparison data in association with each other (S300). In the case ofthe geoid measurement apparatus 10, the inertially-derived data and thecomparison data may be recorded to the recording pan 300 once or inputinto the state variable estimation part 210 in association with eachother. In the case where data is recorded to the recording part 300, therecording part 300 records the inertially-derived data, namely the datarelated to velocity, position, and attitude angle acquired based on theoutput of the inertial measurement part 110 having the three-axis gyroand the three-axis accelerometer attached to the moving body, and thecomparison data, namely the data related to velocity acquired from asource other than the inertial measurement part 110, in an associatedstate. Note that the recording part 300 itself of the geoid calculationdata collection device 100 may be moved and incorporated into the geoidestimation device 200, or the data recorded to the recording part 300 ofthe geoid calculation data collection device 100 may be transmitted tothe recording part 300 of the geoid estimation device 200 over anetwork.

The state variable estimation part 210 uses the inertially-derived dataand the comparison data to apply a Kalman filter in which a plumb linedeviation is included in state variables, and thereby estimates thestate variables including the plumb line deviation (S210). In the Kalmanfilter, at least the plumb line deviation, velocity, position, andattitude angle are included in the state variables. As the plumb linedeviation, it is sufficient for the plumb line deviation in thenorth-south direction and the plumb line deviation in the east-westdirection to be included in the state variables. Consequently, the errorin the inertially-derived data and the plumb line deviation can beestimated. Note that in the Kalman filter, a gravity anomaly componentmay also be included in the state variables. In the case of the geoidmeasurement apparatus 10, the error in the inertially-derived datacalculated based on the estimated state variables may also be suppliedto the inertial measurement data acquisition part 120 or the inertialmeasurement part 110 as feedback. By supplying feedback in this way,hybrid technology like that of Patent literature 1 or Non-patentliterature 1 can be used. Consequently, because the data related tovelocity, position, and attitude angle acquired by the inertialmeasurement data acquisition part 120 can be corrected using theestimated state variables, a change in geoid height can be measuredwhile also correcting the state.

The geoid calculation part 220 calculates a change in geoid height basedon the estimated plumb line deviation at the estimated position that theestimating applied to (S220). It is sufficient to estimate the plumbline deviation in the north-south direction and the plumb line deviationin the east-west direction as the “plumb line deviation”. Note that therecording part 300 may also record information about the geoid heightwith respect to a predetermined reference position, such as the geoidheight of a benchmark. In this case, it is sufficient for the geoidcalculation part 220 to calculate the geoid height at each of theestimated positions based on the information about the geoid height atthe predetermined reference position. For example, if the moving bodymoves along a path that includes one benchmark, one geoid height on thepath is known. For other points on the path, it is sufficient tocalculate the geoid height at each point from the difference withrespect to the point with the known geoid height. Particularly, in thecase where an automobile or a train is used as the moving body and theposition information from a source other than the inertial measurementpart 110 is obtained by GPS, latitude, longitude, and ellipsoidal heightcan be acquired as the comparison data. In addition, because the geoidheight is also understood, the elevation with respect to the latitudeand longitude can also be calculated.

According to the geoid calculation data collection device 100, becausethe inertial measurement part 110 has a bias stability that allows errorarising from the plumb line deviation in the north-south direction andthe plumb line deviation in the east-west direction to be distinguishedto a predetermined degree, the data needed to calculate a change ingeoid height can be collected. According to the geoid measurementmethod, the geoid measurement apparatus 10, and the geoid estimationdevice 200 of the present invention, by using inertially-derived dataand comparison data to apply a Kalman filter in which the plumb linedeviation is included in the state variables, the state variablesincluding the plumb line deviation are estimated, and therefore a changein geoid height can be calculated. Note that even if the geoid height isunknown, if the change in geoid height is understood, the geoidmeasurement method, the geoid measurement apparatus 10, the geoidestimation device 200, and the geoid calculation data collection device100 of the present invention can be used for purposes such as searchingfor resources.

<Theoretical Explanation and Simulation>

The velocity equation in aviation coordinate systems is given by

{dot over (v)} _(eb) ^(n) =C _(b) ^(n) f ^(b)−(2ω_(ie) ^(n)+ω_(en)^(n))×v _(eb) ^(n) +g ^(n)  [Formula 1]

The subscripts n, e, and b denote the navigation coordinate system, theEarth fixed system, and the body coordinate system, respectively.Expressing the components gives

$\begin{matrix}{{\frac{d}{dt}\begin{bmatrix}v_{N} \\v_{E} \\v_{D}\end{bmatrix}} = {{C_{b}^{n}\begin{bmatrix}f_{ibx}^{b} \\f_{iby}^{b} \\f_{ibz}^{b}\end{bmatrix}} - {\left( {{2\begin{bmatrix}{\Omega cos\lambda} \\0 \\{- {\Omega sin\lambda}}\end{bmatrix}} + \begin{bmatrix}\frac{v_{E}}{R_{0} + h} \\{- \frac{v_{N}}{R_{0} + h}} \\{- \frac{v_{E}\tan\;\lambda}{R_{0} + h}}\end{bmatrix}} \right) \times \begin{bmatrix}v_{N} \\v_{E} \\v_{D}\end{bmatrix}} + g^{n}}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Here, v_(N), v_(E), and v_(D) correspond to the northward velocity, theeastward velocity, and the downward velocity, respectively. C_(b) ^(n)is the direction cosine matrix that determines the attitude of the bodycoordinate system with respect to the navigation coordinate system. Theterms f_(ibx) ^(b), f_(iby) ^(b), and f_(ibz) ^(b) express the forcesmeasured by three accelerometers. The terms λ and h denote the latitudeand altitude of the aircraft, while R₀ and Ω express the radius and therotational angular velocity of Earth. If the cross products in theformula are calculated and the plumb line deviations in the north-southdirection and east-west direction are denoted as ξ and η, the followingformula is obtained. In this formula, gravitational changes in thevertical direction (variations from g) am ignored.

$\begin{matrix}{{\frac{d}{dt}\begin{bmatrix}v_{N} \\v_{E} \\v_{D}\end{bmatrix}} = {\quad{{C_{b}^{n}\left\lbrack \begin{matrix}f_{ibx}^{b} \\f_{iby}^{b} \\f_{ibz}^{b}\end{matrix} \right\rbrack} + {\quad{\quad{\begin{bmatrix}{{{- 2}\Omega\; v_{E}\sin\;\lambda} + \frac{{v_{N}v_{D}} - {v_{E}^{2}\tan\;\lambda}}{R_{0} + h} + {\xi\mathcal{g}}} \\{{{- 2}{\Omega\left( {{v_{N}\sin\;\lambda} + {v_{D}\cos\;\lambda}} \right)}} +} \\{{\frac{v_{E}}{R_{0} + h}\left( {v_{D} + {v_{N}\tan\;\lambda}} \right)} - {\eta\mathcal{g}}} \\{{{- 2}\Omega\; v_{E}\cos\;\lambda} + \frac{v_{E}^{2} + v_{N}^{2}}{R_{0} + h} + {\mathcal{g}}}\end{bmatrix}\quad}}}}}} & \left\lbrack {{Formula}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Also, if a gravity anomaly is expressed as S, the following formula isobtained.

$\begin{matrix}{{\frac{d}{dt}\begin{bmatrix}v_{N} \\v_{E} \\v_{D}\end{bmatrix}} = {\quad{{C_{b}^{n}\left\lbrack \begin{matrix}f_{ibx}^{b} \\f_{iby}^{b} \\f_{ibz}^{b}\end{matrix} \right\rbrack} + {\quad{\begin{bmatrix}{{{- 2}\Omega\; v_{E}\sin\;\lambda} + \frac{{v_{N}v_{D}} - {v_{E}^{2}\tan\;\lambda}}{R_{0} + h} + {\xi\left( {{\mathcal{g}} + \delta} \right)}} \\{{{- 2}{\Omega\left( {{v_{N}\sin\;\lambda} + {v_{D}\cos\;\lambda}} \right)}} + \frac{v_{E}}{R_{0} + h} +} \\{\left( {v_{D} + {v_{N}\tan\;\lambda}} \right) - {\eta\left( {{\mathcal{g}} + \delta} \right)}} \\{{{- 2}\Omega\; v_{E}\cos\;\lambda} - \frac{v_{E}^{2} + v_{N}^{2}}{R_{0} + h} + {\mathcal{g}} + \delta}\end{bmatrix}\quad}}}}} & \left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Note that a gravity anomaly is a state variable not used to calculate achange in geoid height, but in the case where the precision of theinertial measurement part is improved, including the gravity anomaly inthe state variables is thought to enable accurate computation of theplumb line deviation.

Similar differential equations also exist for the attitude angle and theposition besides the velocity above, but the differential equationrelated to velocity is the one that affects the plumb line deviation. Inthe present invention, by performing a Kalman filter in which at leasttwo plumb line deviation components are included in the state variablesof the system, it is possible to estimate the state variables includingthe plumb line deviation. Also, if the gravity anomaly is alsoconsidered, there is also a possibility of being able to estimate theplumb line deviation more accurately.

FIGS. 6 to 12 illustrate simulation results related to the measurementof geoid height. FIG. 6 illustrates a case where an inertial measurementpart equipped with a ring laser gyro (RLG) having a level of precisioncomparable to existing technology is installed onboard a vehicle, inwhich position, velocity, and angle data are acquired but comparisondata is not acquired. In the case of the method illustrated in FIG. 6,because comparison data is not acquired, a Kalman filter cannot beapplied. Consequently, the plumb line deviation and the gravity anomalyare not considered, and moreover the state variables are not estimatedby the Kalman filter. The position, velocity, and angle indicate dataacquired by the inertial measurement part. FIG. 7 illustrates an examplein which an inertial measurement part equipped with a ring laser gyrohaving a level of precision comparable to existing technology isinstalled onboard a vehicle, satellite positioning data is used ascomparison data, the same configuration as the geoid measurementapparatus of the present invention is used, and state variablesincluding a plumb line deviation and a gravity anomaly are estimated byapplying a Kalman filter in which the plumb line deviation and thegravity anomaly are included in the state variables to data obtainedfrom a single run. FIG. 8 illustrates an example of measuring geoidheight based on the estimated plumb line deviation in the exampleillustrated in FIG. 7. FIG. 9 illustrates data obtained from 10 runswith the same configuration as FIG. 6. FIG. 10 illustrates an example ofmeasuring geoid height with data obtained from 10 runs with the sameconfiguration as FIG. 8. FIG. 11 illustrates an example of estimatingstate variables including a plumb line deviation and a gravity anomalyby applying a Kalman filter in which the plumb line deviation and thegravity anomaly are included in the state variables to an average ofdata acquired by 100 vehicles with the same configuration as FIG. 8, andestimating geoid height based on the estimated plumb line deviation.FIG. 12 illustrates an example in which an inertial measurement partwhose Allan deviation is improved over existing technology by an orderof magnitude is installed onboard a vehicle, satellite positioning datais used as comparison data, the same configuration as the geoidmeasurement apparatus of the present invention is used, and geoid heightis estimated with data obtained from a single run. In all of thesimulations, the vehicles are made to run for 80 minutes at a speed of50 km/h in the north-south direction. Also, in the example of measuringthe geoid height, the geoid height of a portion of the path is known.The conditions of the simulations in FIGS. 6 to 12 are summarized below.

FIG. 6: vehicles run for 80 minutes at 50 km/h, RLG inertial navigationdevice used, only inertially-derived data used.

FIG. 7: vehicles run for 80 minutes at 50 km/h. RLG inertial navigationdevice and satellite positioning used, satellite positioning performedevery 10 seconds, Kalman filter applied to estimate state variables.

FIG. 8: vehicles run for 80 minutes at 50 km/h, RLG inertial navigationdevice and satellite positioning used, satellite positioning performedevery 10 seconds, Kalman filter applied to estimate state variables,geoid height calculated.

FIG. 9: vehicles run for 80 minutes at 50 km/h, RLG inertial navigationdevice used, only inertially-derived data used, 10 runs of data used.

FIG. 10: vehicles run for 80 minutes at 50 km/h, RLG inertial navigationdevice and satellite positioning used, satellite positioning performedevery 10 seconds, Kalman filter applied to estimate state variables,geoid height calculated, 10 runs of data used.

FIG. 11: vehicles run for 80 minutes at 50 km/h, RLG inertial navigationdevice and satellite positioning used, satellite positioning performedevery 10 seconds, Kalman filter applied to estimate state variables,geoid height calculated, data from 100 vehicles averaged.

FIG. 12: vehicles run for 80 minutes at 50 km/h, inertial calculationpart with Allan deviation improved by an order of magnitude andsatellite positioning used, satellite positioning performed every 10seconds, Kalman filter applied to estimate state variables, geoid heightcalculated, measurement performed once.

In each of the graphs in FIGS. 6 to 12, the horizontal axis representsthe travel distance (km). The vertical axes represent (A1) variation inposition in the forward direction (m), (B1) variation in position in thewidth direction (m), (C1) variation in position in the verticaldirection (m), (A2) variation in speed in the forward direction (km/h),(B2) variation in speed in the width direction (km/h), (C2) variation inspeed in the vertical direction (km/h), (A3) to (C3) variation in theattitude angle (degrees), (A4) plumb line deviation ξ in the north-southdirection (seconds of arc (SOA)), (B4) plumb line deviation η in theeast-west direction (SOA), (C4) gravity anomaly (g), and (D) change ingeoid height or the geoid height (m). Note that (A3) illustrates theEuler angle φ, (B3) illustrates the Euler angle θ, and (C3) illustratesthe Euler angle ψ. The lines labeled [1] in (A4) and (B4) of FIG. 6illustrate the actual values set in the simulation (the plumb linedeviations that match in the case where accurate simulation isachieved). FIGS. 7 to 12 also illustrate similar lines, but [1] isomitted where labeling is difficult. The lines labeled [2] in (A4) and(34) of FIG. 7 illustrate the estimated plumb line deviation. The sameis true of FIG. 8. In the simulations illustrated in FIGS. 6 and 9, theplumb line deviation is not estimated. The lines not labeled [1] in (A4)and (B4) of FIG. 10 are the estimated plumb line deviation. In FIGS. 11and 12, the actual values and the estimated plumb line deviation aresubstantially aligned, and therefore the labels [1] and [2] are omitted.The line labeled [3] in (D) of FIG. 8 illustrates the actual geoidheight set in the simulation. The line labeled [4] illustrates thecalculated geoid height. In (D) of FIG. 10, the line not labeled [3] isthe calculated geoid height. In FIGS. 11 and 12, the actual geoid heightand the calculated geoid height are substantially aligned, and thereforethe labels [3] and [4] are omitted. The geoid height can be calculatedby taking the path integral of the estimated plumb line deviation. Inthe simulations, because the vehicles run north-south, the geoid heightis calculated from the path integral of the north-south plumb linedeviation ξ.

In the simulation illustrated in FIG. 6, because the state variables arenot estimated, the error in the inertially-derived data, the plumb linedeviation, and the gravity anomaly cannot be estimated. Consequently,the plumb line deviation in the north-south direction, the plumb linedeviation in the east-west direction, and the gravity anomaly are “0”.In the simulation illustrated in FIG. 7, the state variables includingthe plumb line deviation and the gravity anomaly are estimated.Consequently, the error in the inertially-derived data, the plumb linedeviation, and the gravity anomaly can be estimated. Also, theinertially-derived data is corrected using the estimated statevariables. However, because the inertially-derived data islow-precision, as (A4) and (B4) of FIG. 7 demonstrate, the plumb linedeviation in the north-south direction and the plumb line deviation inthe east-west direction are different from the line labeled [1] thatillustrates the actual values. FIG. 8 is an example of measuring geoidheight based on the estimated plumb line deviation illustrated in FIG.7. Because the inertially-derived data is low-precision, as illustratedin (D) of FIG. 8, the calculated geoid height is totally different fromthe actual geoid height. In the simulation illustrated in FIG. 9, 10runs of data measured with the same configuration as FIG. 6 areillustrated. As (A1) to (A3), (B1) to (B3), and (C1) to (C3) of FIG. 9demonstrate, even though the same path is measured with the sameconfiguration, there are large inconsistencies in the measurement data.FIG. 10 illustrates the data obtained from 10 runs of a process similarto FIG. 8. As (A4), (B4), and (D) of FIG. 10 demonstrate, the plumb linedeviation in the north-south direction, the plumb line deviation in theeast-west direction, and the geoid height have extremely largeinconsistencies. FIG. 11 uses the average of the data from 100 vehicles.Because the average of data measured from 100 repeated runs is used, theprecision of the inertially-derived data is improved tenfold. As (A4),(B4), and (D) of FIG. 11 demonstrate, the calculated plumb linedeviation in the north-south direction, plumb line deviation in theeast-west direction, and geoid height substantially match the actualvalues. In other words, the above demonstrates that if the precision ofthe inertially-derived data is improved by an order of magnitude overthe related art, a change in geoid height similar to the actual changein geoid height can be measured. In FIG. 12, the precision of theinertial measurement part has been improved by an order of magnitude,and therefore the data obtained from a single run yields a resultsimilar to FIG. 11.

In the case of using a typical gyro commercially available at the timeof the present application, the geoid measurement method, geoidmeasurement apparatus, geoid estimation device, and geoid calculationdata collection device of the present invention can be implemented byreducing error through repeated measurement. Also, if measures such asincreasing the diameter of a ring laser gyro are taken, the geoidmeasurement method and the like of the present invention can beimplemented even without performing repeated measurement.

For example, if the geoid measurement apparatus of the present inventionhaving an inertial measurement part with improved precision is installedonboard an automobile and driven between two benchmarks, the continuousgeoid height can be measured easily. Furthermore, if GPS information isalso used, the continuous elevation is also understood easily. Also, ifthe geoid measurement apparatus of the present invention having aninertial measurement part with improved precision is installed onboard atrain and driven periodically, a change in geoid height can be measuredperiodically. Consequently, there is a possibility of being able toobserve the movement of Earth's crust or the ground.

DESCRIPTION OF REFERENCE NUMERALS

-   10 geoid measurement apparatus-   100 geoid calculation data collection device-   110 inertial measurement part-   120 inertial measurement data acquisition part-   130 comparison data acquisition part-   200 geoid estimation device-   210 state variable estimation part-   220 geoid calculation part-   300 recording part

What is claimed is:
 1. A geoid calculation data collection devicecomprising: an inertial measurement data acquisition part that acquiresdata related to velocity, position, and attitude angle asinertially-derived data based on an output of an inertial measurementpart having a three-axis gyro and a three-axis accelerometer attached toa moving body; a comparison data acquisition part that acquires datarelated to velocity as comparison data from a source other than theinertial measurement part; and a recording part that records theinertially-derived data and the comparison data in association with eachother, wherein the inertial measurement part has a bias stability thatallows error arising from plumb line deviation to be distinguished to apredetermined degree.
 2. The geoid calculation data collection deviceaccording to claim 1, wherein the inertially-derived data and thecomparison data is used to apply a Kalman filter in which the plumb linedeviation is included in the state variables in order to estimate statevariables including a plumb line deviation.
 3. A geoid calculation datacollection device comprising: an inertial measurement data acquisitionpart, provided with an inertial measurement part having a three-axisgyro and a three-axis accelerometer to be attached to a moving body, andthat acquires data related to velocity, position, and attitude angle asinertially-derived data; a comparison data acquisition part thatacquires data related to velocity as comparison data from a source otherthan the inertial measurement part; and a recording part that recordsthe inertially-derived data and the comparison data in association witheach other, wherein the inertial measurement part has a bias stabilitythat allows error arising from plumb line deviation to be distinguishedto a predetermined degree.
 4. The geoid calculation data collectiondevice according to claim 3, wherein the inertially-derived data and thecomparison data is used to apply a Kalman filter in which the plumb linedeviation is included in the state variables in order to estimate statevariables including a plumb line deviation.